The hat does come with the riveted clip, but not the stud and wingnut. I'm guessing those are still on your old engine, along with your original intake manifold, which probably should have been switched over to the "new" engine. If it had EGR, but doesn't now, it's probably going to give you a code and a CEL. I don't know where you live but, if you have smog inspections, it won't pass.

Basically, any air that gets into the intake without first passing through the MAF will be unmetered and cause the engine to not run properly. The reason it stalls when the hat comes off is that the engine gets a big gulp of air that the ECM doesn't "know" about, so it doesn't add any gas to compensate. That might be a little oversimplified, but those are the basics.

 

You're missing the rear fastener for the throttle body that has a stud on top of it for a riser adapter which is where the wingnut for the air cleaner adapter attaches (so 3 pieces total missing at the back). It also looks like your 'hat' is missing the metal piece that is supposed to be riveted to the front and also has a busted out hole at the rear so I'd get a replacement for that as well.

The missing throttle body bolt is nice considering you paid someone to install an engine with missing, kind of critical components. Good attention to detail right there. I'd wonder what else they failed to notice. If it were my money, I would be making them fix it. While they were at it, they should have swapped out the van dip stick (made for access under the stubby hoods on vans) with that of the trucks/suvs from your old engine or a new component that costs a mere $20 GM MSRP or $10 for an aftermarket equivalent

As Tom A said, a loose intake duct at the throttle body would definitely cause the symptoms you're experiencing as the PCM isn't seeing all of the air the engine is ingesting passing through the MAF sensor as it expects it to for proper engine management. Perfectly normal. Besides, who wants unfiltered air entering the engine they just paid to have installed...

Everything you're missing can be found either on your old engine or at your local junkyard provided they have anything s-series with a 4.3v6 from '96 to '04 and you take the initiative to go get it. Or you could go with original parts for the AIR INTAKE. I couldn't find the proper diagram showing the throttle body fasteners. Hopefully your mechanic didn't just cover up some other problem (e.g. stripped or otherwise screwed up insert in the upper intake plenum) with the used engine without informing you about it...

 

i would 'liberate' your old motor from the "mechanic" that did the swap. and then pull the stud and air cleaner 'hat' off the old one, from the looks of it they did not know how to get the cleaner adapter off and just cut the damn thing.

 

Hi there. Presently.. When I unplug this sensor.. it sets a code, yes, but it idles fine and does not stall at lights.

When I plug it back in, it runs somewhat irregularly, surges sometimes, sometimes stalled at lights, and makes an intermittent misfire that seems to be localized to Cylinder #2. But it does not misfire all the time. (Thankful to the Lord for that.)

What is that sensor called? And what is up with the intermittent misfiring, that started as P0300 ?

 

That is your MAF sensor, as in Mass Airflow Sensor. I would do a search on here as more than a few folks have had the same problem you are now experiencing. First thing I would do is to clean the wire, again, do a search as this has been covered many times on here.

 

As AJ said, MAF, or Mass Air Flow. And you can try pulling it off and cleaning it, there are spray cleaners specifically for it. If you end up replacing it, I would suggest trying to buy an OEM used one from a junk yard before putting a brand new aftermarket one made in China on it. The original ones really don't have too many issues, it's not super common for them to actually go bad. But the knock-offs are known to give people issues...

The engine computer relies on readings from the MAF to adjust fuel delivery and spark. A misreading one because it's dirty or if it's just bad, can definitely cause worse running conditions if it's plugged in because it's sending bad readings to the engine computer. When it's unplugged, the computer resorts to a default set of parameters, that although are not optimized and that's what will cause the running issues and terrible gas mileage with it unplugged, it will at least run.

 

This is why creating numerous threads for related questions is an issue... No link to the back-story. *Combining with the air filter adapter thread*

While cleaning the MAF might be a good idea if diagnosis shows that it is an issue, if not done carefully, you could damage it rendering it inoperable. So until you fix the other glaringly obvious issues with the intake ductwork and missing throttle body retaining bolt, I wouldn't poke that bear...

As far as running with the MAF disconnected... You certainly can, but as I stated previously, I would not recommend driving the truck around with a massive unfiltered air leak in the intake ductwork that could suck in all kinds of unknown crap floating around under the hood. That is unless you want to be looking for another engine if something nasty gets pulled in. Currently, the closest thing holding your 'hat' on is your hood...

 

Okay, cool. I actually did also obtain the screw. I ca. try cleaning it carefully...

My only next question would be.. would a wonky MAF sensor also give random misfires?

 

The best way to clean it is with one of the aerosol products available specifically for that purpose.

And a bad MAF can cause random misfires if it causes the engine to run too lean. But a loose intake "hat" can cause the exact same symptoms.

 

It seems to drive just fine with that sensor unplugged.